Separated Electric Motor Assisted Propulsion for Human-Powered Watercraft

ABSTRACT

A propulsion system for hybrid electric watercraft for personal enjoyment that incorporates human power with electric motor assistance, energy storage and optional solar power to achieve increased watercraft speeds and/or reduced pedaling effort. Control electronics enable operator-adjustable electric motor assistance to the propulsion, thereby providing flexible pedal cadences and efforts and enjoyment for a wide variety of operators. An optional photovoltaic solar panel augments the power generation to extend travel time with motor assistance, and recharges the energy storage system. This invention enables a pleasure watercraft that is simultaneously lightweight, low cost, low maintenance, environmentally friendly with zero pollution, ultra-low noise, and thrilling to operate, while simultaneously providing a means of enjoyable exercise for operators of nearly all abilities.

FEDERALLY SPONSORED RESEARCH

Not Applicable

SEQUENCE LISTING OR PROGRAM

Not Applicable

BACKGROUND

1. Field of Invention

The present invention relates to the general art of watercraft, and tothe particular field of hybrid-electric powered watercraft incorporatinghuman (e.g., pedal) power with electric motor power assistance withenergy storage in the form of electric battery, capacitor, fuel cell,and/or flywheel energy storage, and/or solar power.

2. Description of Prior Art

A multitude of pedal-powered watercraft (also referred to as waterbikes, water-bicycles, and watercycles) are commercially available. Theyare relatively low cost, low maintenance, light weight, and fun. Theirmain drawback is the relatively low power output capability of theoperators. Unlike watercraft propelled by conventional combustionengines, pedal-powered watercraft are severely limited in powercapability; typically less than 200 watts (around ¼ hp) per person on acontinuous basis. A cyclist in good condition can generate around 200watts at a preferred cadence of around 90-100 RPM. Many people of lesserabilities may be only capable of generating around 100 watts in acontinuous comfortable manner. Thus maximizing the overall efficiency ofthe watercraft, including its propulsion system, as it travels in wateris vitally important to maximize speed and travel distance capabilities.To maximize the speed (and pedaling efficiency), many of the newerwatercycles, such as the Seacycle® and Waterbike® manufactured by theMeyers Boat Company, Inc. and the Surfbike, are designed to be aslightweight with efficient long and narrow hulls.

OBJECTS AND ADVANTAGES

The object of the invention is to provide a propulsion system enabling apleasure watercraft that is simultaneously lightweight, low cost,environmentally friendly with zero pollution, ultra-low noise, andthrilling to operate, while simultaneously providing an optional meansof enjoyable exercise for operators of all abilities. A person thatroutinely pedals a conventional watercycle on a specific lake or riveris likely to see only the same limited area each time, due to theseverely restricted speed, and hence, travel distance possible within afinite amount of exercise time. This can lead to boredom rapidly. Thusone objective of the present invention is to provide a new type ofwatercycle employing an electric motor assistance means with energystorage and/or solar power to substantially increase the speed and rangeof the watercraft.

With proper hull design and sufficient electric motor assistance, thisinvention may enable the watercraft to achieving hull planing speeds,that would normally not be possible under human-power only.

This invention combines human-power and electric-power watercrafttechnologies into one watercraft, and by adding new innovative controls,the best of both types of watercraft is obtained. With this invention,the fit cyclist that routinely exercises, as well as the occasionalrider, can explore a much larger area of a bay, lake or river, in ashorter amount of time, thereby increasing enjoyment considerably.Unlike battery-only electric watercraft, this invention removes theworry of running out of battery power, or solar power on a cloudy day ornight. If the batteries become drained, and solar power is notavailable, the operator can still pedal back to shore, though at reducedpower. Diagnostic displays that monitor the usable stored energy of thebattery, as well as the generated solar power and pedal power, keep theoperator informed, so that the operator can wisely return to shore underfull power, if desired, prior to battery depletion.

It is another objective of the present invention to provide a propulsionsystem for watercraft comprising electric motor assistance, therebypermitting operators of differing physical abilities and goals tosimultaneously operate one or more of the watercraft over the samedistance at the same speed, thereby sharing the experience, while stillexercising at their individually preferred effort levels.

It is another objective of the present invention to provide a propulsionsystem for dual-seated watercraft comprising electric motor assistance,thereby permitting operators of differing physical abilities and goalsto simultaneously operate the same watercraft while each independentlyachieving their desired level of physical exercise, without sacrificingthe overall speed or travel distance of the watercraft.

It is still another objective of the present invention to provide apropulsion system for watercraft comprising operator-selectable pedaltorque vs. pedal cadence characteristics, such as simulated rollinghills to add an additional degree of enjoyment and pedaling comfort tothe operator. Such flexibility is not possible with puremechanically-driven systems, such as prior art waterbikes.

Yet another objective of the present invention is to provide apropulsion system for watercraft employing an electric motor assistancemeans via energy storage with photovoltaic power to recharge the energystorage, thereby providing a pollution-free watercraft.

Yet another objective of the present invention is to provide apropulsion system for watercraft employing an electric motor assistancemeans via energy storage with photovoltaic power to enable increasedtravel speed and range when the energy storage system is depleted.

Yet another objective of the present invention is to provide apropulsion system for an electric watercraft that can be optionallyoperated solely from stored energy or on-board photovoltaic power.

Yet another objective of the present invention is to provide apropulsion system for a hybrid-electric watercraft with mechanicallinkage connecting a pedal mechanism to a propeller such that thewatercraft can still be propelled under human power in the event of afailure of an electric or electronic component.

Yet another objective of the present invention is to provide apropulsion system for a motor-assisted watercycle wherein the pedalmechanism is operated by an operators hands/arms, thereyby significantlyincreasing the speed and travel range of the watercycle, compared to awatercycle without this invention.

SUMMARY

A propulsion system for watercraft comprising at least one human-poweredpropulsion means, at least one electric motor-powered propulsion means,the said electric motor-powered propulsion means configured to providepropulsion as a function of the state of the said human-poweredpropulsion means, whereby the electric motor-powered propulsion assiststhe human-powered propulsion means. The propulsion system furthercomprising a sensing means configured to provide a signal indicative ofthe state of the human-powered propulsion means, and a control meansconfigured to receive the said signal and to control the state of thesaid electric motor-powered propulsion means according to the saidsignal. The electric motor-powered propulsion means is furtherconfigured to be a function of the said signal and anoperator-adjustable motor assistance factor.

DRAWINGS Drawing Figures

FIG. 1 illustrates a typical human-powered watercraft of the prior art(U.S. Pat. No. 5,672,080).

FIG. 2 illustrates the propulsion system unit of the human-poweredwatercraft of the prior art with chain and sprocket drive mechanisms(U.S. Pat. No. 5,672,080).

FIG. 3 illustrates the power and control system functional block diagramfor the preferred embodiment of this invention for a single operator.

FIG. 4 illustrates the propulsion system unit of the prior art modifiedwith the addition of a pedal-effort (e.g., cadence or speed) sensor inaccordance with this invention.

FIG. 5 illustrates a watercraft utilizing the propulsion systemincorporating electric motor assistance.

FIG. 6 illustrates the power and control system functional block diagramfor the preferred embodiment of this invention for two operators.

FIG. 7 illustrates the propulsion system unit of the prior art modifiedwith the addition of a pedal-effort (e.g., propeller shaft torque)sensor in accordance with this invention.

FIG. 8 illustrates the operator control and display unit for asingle-operator/single-motor embodiment.

FIG. 9 illustrates the operator control and display unit for adual-operator/single-motor embodiment.

DETAILED DESCRIPTION Description and Operation

FIG. 1 illustrates a typical human-powered watercycle (water bicycle) 1of the prior art (U.S. Pat. No. 5,672,080). The watercycle 1 has anelongated floatation board 3, a propulsion and seat unit 7, and asteering unit 9. The propulsion and seat unit 7 comprises of an operatorseat 6 and a human-powered mechanical propulsion unit 12. The propulsionunit 12 comprises of an upper body 11 and lower body 19, pedal mechanism15, and propeller 21. An operator pedals the crank pedal mechanism 15,which turns the propeller 21, thereby propelling the watercraft forward.

FIG. 2 illustrates the propulsion system unit 12 of the human-poweredwatercycle 1 of the prior art in FIG. 1. A human operator pedals a crankpedal mechanism 15, thereby causing a crankshaft 16 to rotate inequivalent manner as pedaling the crank mechanism of a bicycle. Thecrankshaft contains a crankshaft sprocket 17. A propeller 21 is mountedon a rotating propeller shaft 42 that also contains a propeller shaftsprocket 25. Bearings 32 and 33 support the propeller shaft 42. Thecrankshaft sprocket 17 and the propeller shaft sprocket 25 are linked bya chain 23, which transmits the pedaling motion power from thecrankshaft 16 to the propeller shaft 42 and propeller 21, and causingthe propeller to rotate, produce thrust, and propel the watercycle. Thedirection of thrust and resulting watercycle motion is controlled simplyby the direction of the pedaling action by the operator.

The relative sizes of the crankshaft sprocket 17 and propeller shaftsprocket 25 dictate an effective “gear” ratio for the pedaling action.Typical gear ratios range from 1:5 to 1:10 (with propeller rotationalspeed increased relative to pedal cadence), and are chosen dependentupon the size and pitch of the propeller, and in some cases, thecustomization of the propulsion system for specific operators. Thepropulsion system in FIG. 2 is single-speed, i.e., no gear ratio(sprocket) changing, unlike multiple speed bikes. This is the mostcommon configuration, although multi-speed system are available,however, pedaling in reverse direction is generally not possible.

The propulsion unit housing 19 is usually molded or cast from a polymersuch as nylon, HDPE, or urethane. The propeller 21 is usually molded orcast from a polymer such as nylon or urethane. The propeller shaft 42 isusually fabricated from stainless steel. The chain 23 and sprockets 17and 25 are usually steel, with a heavy weight oil or grease applied forlubrication and corrosion protection.

FIG. 3 is a block diagram illustrating the preferred embodiment of apropulsion system 100 for a watercycle that incorporates electric motorpropulsion assistance. The propulsion system 100 comprises of amechanical propulsion unit 13 powered entirely by human power viapedal/crank system 15, shaft 42 and propeller 21, the same or similar tothe propulsion unit 12 of the prior art as illustrated in FIG. 2. Inaddition, an electric propulsion unit 88 comprises of an electric motor34 driving a propeller 36 via shaft 99. The electric propulsion unit 88is mechanically isolated, and preferably in a separate housing, from themechanical propulsion unit 13. An electronic control unit 52 providescontrolled power to the electric motor 34 from an energy storage unit56, as well as connects to an operator-interface 58.

As also illustrated in FIG. 4, a pedaling-effort sensor 46 is locatedwithin the mechanical propulsion unit 13 and provides pedal mechanismrotation speed (e.g., cadence) and rotation direction information to theelectronic control unit 52 of FIG. 3. The sensor 46 is preferably aquadrature gear-tooth sensor providing voltage pulses for each passingof the teeth of crankshaft sprocket 17. The quadrature pulse signals aredecoded to obtain rotation speed and direction information.Alternatively, it can provide a signal similar to that of a tachometer,in which a voltage is generated whose magnitude and polarity isproportional to the velocity of the passing teeth of the sprocket 17.Commercially available sensors and the means to obtain speed anddirectional information are well established in industry. Alternativemean include, but are not limited to, sensing of the teeth passing ofthe propeller shaft sprocket 25 or a via tachometer, encoder or resolverdirectly coupled to the propeller shaft 42 or crankshaft 16.

FIG. 5 illustrates a watercraft 14 of the prior art (from FIG. 1)modified to incorporate this invention. The watercraft is fitted withthe propulsion unit 13 and the operator control unit 58, allinterconnected via the appropriate power and control wiring (not shown).The energy storage unit 56 is shown to be located attached to the hull3. The electric propulsion unit 88 comprising of electric motor 34 andpropeller 36 are located in a propulsion motor housing 37 attached tothe hull 3.

The electric motor 34 may be of any type including brushed DC, brushlessDC, permanent magnet (PM) AC synchronous, induction, switchedreluctance, and synchronous reluctance. The preferred types arebrushless DC and PM AC synchronous because they generally provide thehighest power density with the highest efficiency. Furthermore, themotors are inherently rugged and relatively simple to construct. Anotheradvantage is that the stator windings can be effectively cooled from thesurrounding water by fabricating the motor housing 37 from aluminum orsteel. Anodized aluminum is preferred for the motor housing 37 becauseit is lightweight, corrosion resistant, easy to machine, and has highthermal conductivity.

Brushed DC motors are also a favorable motor type due to their inherentlow cost and simple controllers.

The design ratings for the electric motor are dependent upon the levelof performance desired for the specific product. A typical embodimentrating would be in the range of 250 to 1000 Watts, at a rated speed inthe range of 400 to 1500 RPM assuming direct coupling between thepropeller 36 and the electric motor rotor 34.

The electronic control unit 52 (FIG. 3) includes a system controlelectronics unit 62 and a propulsion control electronics unit 64. Thesystems control electronics unit 62 preferably contains amicrocontroller, such as the Zilog ZNEO Z16F, or a DSP, such as theTMS320C24x. The systems control electronics unit 62 interfaces/monitorsa user (operator) interface unit 58. The primary function of the systemscontrol electronics unit 62 is to monitor the state of the mechanicalpropulsion unit 13 via sensor 46 and provide a corresponding motorcommand signal. In the preferred embodiment, the sensor 46 provides asignal that is indicative of the rotational speed of the mechanicalpropulsion unit 13, and the systems control electronics unit 62,receives sensor 46 signal, and then creates a motor speed commandsignal, ω_(motor)*. The relationship between the speed of the mechanicalpropulsion unit 13 and the motor speed command, ω_(motor)*, is set by auser (operator) setting via the interface unit 58.

For example, with the sensor 46 measuring the speed (cadence) of thepedaling effort, ω_(pedal), the motor speed command is:

ω_(motor)*=ω_(prop36) *=K _(assist) N _(ped) _(—) ₃₆ω_(pedal)   1

where ω_(prop36)* is the rotational speed of propeller 36, K_(assist) isa motor assistance factor set by the user, and N_(ped) _(—) ₃₆ is afixed speed ratio (constant factor) between the pedal cadence and motorspeed that incorporates the effective gear ratio of propulsion unit 13and the relative sizes of propellers 21 and 36.

Note in the preferred embodiment, the propeller 36 is directly coupledto the electric motor 34 (via shaft 99), hence ω_(motor)=ω_(prop36) andω_(motor)*=ω_(prop36)*. In alternative embodiments, the propeller can beindirectly coupled to the motor via gearing, sprockets and chains,pulleys and belts, etc., in which case, an additional “gear” ratio wouldbe incorporated into equation 1.

The factor N_(ped) _(—) ₃₆ can be considered as comprising of two parts;

N_(ped) _(—) ₃₆=N_(ped) _(—) _(GR)N₂₁ _(—) ₃₆   2

where N_(ped) _(—) _(GR) is the effective gear ratio between sprockets17 and 25 of the propulsion unit 13 and N₂₁ _(—) ₃₆ is the ratio of therated (or optimal) speeds of the propellers 36 and 21, respectively.

Alternatively, if the sensor 46 measures the speed of the propeller 21,ω_(prop21), directly, then simply

ω_(motor)*=ω_(prop36) *=K _(assist) N ₂₁ _(—) ₃₆ω_(prop21)   3

For example, if propellers 21 and 36 are identical, then N₂₁ _(—) ₃₆=1.In which case, for a value of K_(assist)=100%, the propellers 21 and 36would operate at the same speed. Similarly, for a value ofK_(assist)=200%, propeller 36 would rotate at twice the speed ofpropeller 21. If for example, the rated speed for propeller 36 is twicethat of propeller 21, then N₂₁ _(—) ₃₆ would be 2.

The selection of propellers 21 and 36 depends upon many factors that arepreferably taken into account during the propulsion system design phase.These factors include the desired motor rating, speed, and motorefficiency, the respective propeller efficiencies, the amount of energystorage desired, the available gear ratio in propulsion unit 13, andmany more. Faster motors tend to be smaller and lower cost than slowermotors for the same power ratings. Likewise, smaller propellers tend torun faster than larger propellers for the same power and thrust rating.However, smaller, fast-turning propellers also tend to have lowerefficiency than larger, slower-turning propellers. Hence, a fast turningpropeller 36 design may result in a lower cost electric propulsion unit88, but additional energy storage would be required due to the lowerefficiency. Thus an overall system optimization is preferable todetermine the lowest cost system while still meeting the desired marketdemands. Such capabilities are within the skill set of one skilled inthe art of electric motor systems and marine propulsion design.

Note that the motor speed command, ω_(motor)*, may also simply be amotor frequency command if the motor 34 is an AC motor, or a voltagecommand if the motor is a DC motor.

Since propeller (and propulsion) power is proportional to the cube ofthe propeller speed, for a K_(assist) value of 200%, the propulsionpower of propeller 36 would be 2̂3=8 times the pedal power exerted onpropeller 21. The speed of a watercraft is proportional to the cubicroot of net propulsion power (from propellers 21+36), so that theresulting watercraft speed would be roughly directly proportional to theK_(assist) factor as defined above.

In general, the propulsion system comprises of a human-poweredpropulsion means, an electric motor-powered propulsion means, a sensingmeans configured to provide a signal indicative of the state of thehuman-powered propulsion means, and a control means configured toreceive the signal and to control the state of the electricmotor-powered propulsion means according to that signal. The state ofthe human-powered propulsion means can be any state indicative of thepedaling effort or propeller 21; including, but not limited to, a speedvalue, ω_(pedal) or ω_(prop21), a pedal torque value, a propeller 21torque value, a pedal power value, or a propeller 21 power value.

As one alternative embodiment, the K_(assist) factor can be defined tobe applied to the sensed or estimated pedal torque, T_(pedal), andthereby, yielding a motor torque command, T_(motor)*; e.g.,

$\begin{matrix}{T_{motor}^{*} = {\frac{K_{assist}}{N_{ped\_ GR}}T_{pedal}}} & 4\end{matrix}$

The electric motor 34 would then be torque controlled, rather than speedcontrolled; both of which are well known in industry. Or, as anotheralternative, the K_(assist) factor can be defined to be applied to thesensed or estimated pedal power, P_(pedal), or propeller 21 power,P_(prop21), and yielding a motor power command, P_(motor)*; e.g.,

P _(motor) *=K _(assist) P _(pedal)   5

P _(motor) *=K _(assist) P _(prop21)   6

The systems control electronics unit 62 (FIG. 3) sends the electricmotor control commands (e.g., ω_(motor)* or T_(motor)* or P_(motor)*,etc.) to the propulsion control electronics unit 64. Thus the electricmotor propulsion unit 64 will track the actions and/or effort of thepedal-powered propulsion unit 13; e.g., when the operator is notpedaling, motor 34 and propeller 36 will also be stopped. When theoperator puts forth effort causing propeller 21 to rotate, motor 34 andpropeller 36 will also rotate at a speed, torque, or power setting thatis a function of the propeller 21 (or pedal) state and the K_(assist)factor as set by the operator. The electric motor propulsion unit willthus act to amplify the effort of the pedal-powered propulsion unit 13,resulting in greater watercraft speed for the same pedaling effort.

For a given propeller 21 size and shape and rotating speed, the pedalingeffort required is partially dependent upon the watercraft speed; i.e.,the slip speed of the propeller through the water. Thus the electricmotor propulsion unit will also provide the benefit of providing somedegree of flexibility for the user in setting the amount of pedalingeffort he/she wishes to produce for any given cadence. The operator can,in effect, adjust an “effective” gear ratio via adjusting the K_(assist)factor, and thus pedal at a preferred cadence vs. torque point.

The propulsion control electronics 64 comprises preferably of a powerelectronic switching converter consistent with the electric motor 34;e.g., for a 3-phase brushless-DC or PM-AC synchronous motor, theconverter would typically be a 3-phase MOSFET PWMvoltage-source-inverter bridge. If the motor 34 is a brushed-DC motor,then the converter would typically be either a DC chopper circuit withMOSFET PWM switching and reversing contactors, or a full H-bridgecircuit, also with MOSFET PWM switching.

In the preferred embodiment, the electronic control unit 52 is simply aPWM motor drive with a microcontroller (or DSP) with sufficientprocessing and I/O, PWM, and A/D ports to generate both the system/motorcontrol commands (e.g., speed, torque or power) and the individual PWMgating signals for the motor drive switches, as well as communicate withthe user (operator) interface 58.

The two units 62 and 64 are preferably integrated into a single printedcircuit board, although they can also be designed to be distinct andphysically separated.

An optional solar electric unit 70, mounted on the watercraft,comprising of at least one solar (photovoltaic) panel 72 and solarcharge control electronics unit 74 is shown in FIG. 3 and FIG. 5. Thesolar electric unit 70 charges the energy storage unit 56, and also cansupply power to the propulsion unit when the watercraft is in operation.

The energy storage unit 56 can be located within or attached to theelectric motor propulsion unit housing 37 to provide a compactpropulsion system with minimal electrical wiring, connectors, andindividual components as seen by the operator. Alternatively, the energystorage unit 56 can be located separate from the propulsion unit housing37, but within or attached to watercraft hull or structure, asillustrated in FIG. 5. This configuration generally enables a largeramount of energy storage.

The energy storage unit 56 is preferably a battery such as NiMH,lead-acid, or NiCad. As battery technology improves and costs reduce andsafety improves, new battery technologies such as large-format Li-Ion orNaNiCl may become cost effective and safe. Alternative energy storageand conversion means such as fuel-cells, ultra-capacitors, and flywheelsmay also become cost effective. The preferred rated voltage for theenergy storage unit 56 is 24V DC, although 12V, 36V, 42V, and 48V DC arealso suitable, as well as values between and above.

The amount of stored energy is preferably at least sufficient to allowoperation with maximum motor assistance for 1-2 hours. The amount ofenergy storage is therefore dependent upon the maximum ratings of theelectric motor 34. For example, if the motor is rated at 250 Watts, thenat least 250-500 Watt-hours of available energy storage capacity isdesired. Likewise, if the motor is rated at 1000 Watts, then at least1000-2000 Watt-hours of available capacity is desired.

The pedaling-effort sensor 46 may alternatively or additionally providepedal mechanism torque and torque direction information to theelectronic control unit 52. As illustrated by the propulsion unit 102 inFIG. 6, the pedaling-effort sensor 46 may alternatively be a torqueand/or speed sensor 55 located near the shaft of the propeller 21 toprovide speed and/or torque information of the propeller 21.

The electronics control unit 52 is shown in FIG. 5 to be optionallylocated below the waterline of the watercraft in the housing 37 toprovide cooling of the power electronic components in the propulsioncontrol electronics unit 64. The MOSFET switching devices are typicallyconnected to the inner surface of an aluminum heatsink or cold plate.The outer surface of the heatsink/cold plate is in direct or at leastindirect contact with the water for good thermal heat transfer from theswitching devices to the water. The outer edges of the heatsink/coldplate are sealed against the propulsion unit housing 52.

An externally located or mounted charging system 82 is used inconjunction, or as an alternative, to the optional solar electric unit70 to charge the energy (e.g., battery) storage unit 56 when thewatercraft is not in operation. The external charging system 82 may beof any type compatible with the voltage rating, storage capacity, andenergy storage type, including a conventional lead-acid (or NiMH,Li-Ion, etc.) battery charger connected to the utility grid, a solarelectric charging system, or a wind turbine power charging system. Ifthe energy storage unit 56 is a fuel cell, then recharging comprisesreplenishing the fuel, e.g., hydrogen, etc.

FIG. 7 illustrates the block diagram of an embodiment 104 designed fortwo operators, comprising two human (pedal) powered propulsion units 13a and 13 b similar to units 13 in FIGS. 3 and 4 or 102 in FIG. 6 oralternative embodiments described prior. A single electric motorpropulsion unit 88 is illustrated, but multiple electric motorpropulsion units are also readily possible and may also be advantageousto achieve higher watercraft velocities. The system control unit 52receives pedal-effort signals from sensors 46 a and 46 b located on thetwo pedal-powered propulsion units. In the preferred embodiment, asingle motor command, ω_(motor)*, is generated by simply taking theaverage of the two sensor outputs; e.g., if the sensors 46 a and 46 bprovide pedal speed signals ω_(pedal46a)* and ω_(pedal46b)*,respectively, then,

$\begin{matrix}{\omega_{motor}^{*} = {\omega_{{prop}\; 36}^{*} = {K_{assist}N_{{ped\_}36}\frac{\left( {\omega_{{pedal}\mspace{11mu} 46a} + \omega_{{pedal}\mspace{11mu} 46\; b}} \right)}{2}}}} & 7\end{matrix}$

Similarly, the motor command may also be in the form of a torque orpower command obtained via an average torque or power from the pedalingeffort, or any of the alternative embodiments described prior.

Based upon the above control description, the preferred systemembodiment works as follows:

-   -   1.) The operator sets the motor assistance level, K_(assist).    -   2.) The operator exerts force on the pedals, which is converted        to an effective torque, thereby causing the propulsion unit 13        to achieve some initial propeller 21 speed, ω_(prop21), and        power, P_(prop21).    -   3.) The controller senses the pedal or propeller speed (or        torque or power) from the pedal effort sensor 46.    -   4.) From the pedal or propeller speed (or torque or power) and        motor assistance level, K_(assist), the controller calculates        and commands the desired motor speed, ω_(motor)* (or torque or        power).    -   5.) The controller 70 sets or regulates the motor voltage and/or        frequency (and/or current) to achieve the desired motor speed        (or torque or power), and hence propeller 36 speed, ω_(prop36),        and power, P_(prop36).    -   6.) The total propulsion power of the watercraft increases to        P_(prop21)+P_(prop36), thereby increasing the speed of the        watercraft; and/or allowing the operator to reduces his/her        pedaling effort to a desired comfort/exercise level while still        maintaining a high watercraft speed.

In actual practice, the control steps 1-6 outlined above occur nearlysimultaneously in a continuous iterative process such the watercraftoperation is entirely smooth and pleasant to operate.

The pedaling through rolling terrain (i.e., “hills” and “valleys”), aswith a bicycle on land, can be simulated for the operator, by allowingthe motor assistance gain, K_(assist), to vary in a sinusoidal (orother) manner as a function of time, distance traveled, or revolutionscount. The operator would set, for example, the amplitude and period(i.e., wavelength) of the rolling terrain.

Increased pedaling and vehicle inertia, similar to that experiencedwhile pedaling a bicycle from standstill or coasting from an establishedspeed, can also be simulated by allowing the motor assistance gain,K_(assist), to vary as a function of watercraft acceleration. Forexample, when the watercraft and/or pedaling action is accelerating, theK_(assist) value can be temporarily reduced, and then graduallyincreased to the operator-set level in an exponential manner, as theacceleration decreases. Likewise, the when the pedaling action isdecelerating, the K_(assist) value can be temporarily increased, andthen gradually decreased to the operator-set level in an exponentialmanner as the deceleration ceases.

FIG. 8 illustrates the user (operator) interface 58, comprising of STARTand STOP switches 83, UP 82 and DOWN 81 switches to set the K_(assist)value, and a LCD character (or graphics) module 59 to display varioususeful information, such as the K_(assist) value, pedal cadence, pedalpower, motor power, and total propulsion power. Other information suchas watercraft speed, propeller RPM, pedal torque, battery status, etc.can also be displayed. The switches can be of a low-cost and weatherresistant membrane switch type.

FIG. 9 illustrates an exemplary operator display and interface designedfor two operators; Left and Right, in accordance with thedual-operator/single-motor system illustrated in FIG. 7. Adual-operator/dual-motor system would utilize a similar operator displayand interface, with the option of displaying data status data of eitheror both propulsion motors.

Knowledge of the watercraft speed is generally of direct interest to theoperator, as well as indirectly. The watercraft speed can be used tocalculate distance traveled, available distance to travel with remainingenergy storage capacity, etc. Such a method is disclosed in U.S. Pat.No. 6,986,688, and can be incorporated in this invention. The propeller36 torque is first calculated from the commanded or estimated electricmotor torque. Then, if the propeller 36 characteristics are known, theactual watercraft speed can be estimated using an equation; e.g.,

$\begin{matrix}{\upsilon_{boat\_ calc} \cong {K_{1}\left( {\omega_{{prop}\mspace{11mu} 36} - \sqrt{\frac{T_{{prop}\mspace{11mu} 36{\_ calc}}}{K_{0}}}} \right)}} & 8\end{matrix}$

where K₀ and K₁ are known parameters characterizing the propeller 36.

To reverse the watercraft, the operator preferably reverses thedirection of the pedaling effort. The system control electronics unit 62detects via sensor 46 that the pedal rotation has reversed (or that thetorque signal from optional torque sensor 55 has reversed), and thensends a negative motor speed (or torque or power) command to thepropulsion control electronics unit 64, thereby causing the electricmotor torque to reverse also.

Prior to the start of normal operation, the energy storage unit 56 ispreferably to be charged to its full capacity. During normal operationwith K_(assist) values above 0%, the energy stored in the energy storageunit 56 will be continuously depleted at a rated dependent upon theK_(assist) value chosen by the operator and by the pedaling effort putforth. The system control electronics unit 62 will preferably continueto monitor the charge state of the energy storage unit 56, and notifythe operator of the charge state via the user interface 58 LCD display59.

In embodiments whereby a photovoltaic charge unit 70 is not includedwith the watercraft, when the charge in the energy storage unit 56 isdepleted, or at/below a predetermined lower threshold, the systemcontrol electronics unit 62 will preferably set the K_(assist) value tozero and no longer command a non-zero motor torque. The operator willthen be responsible for propelling the watercraft solely from pedaling.

In embodiments whereby a photovoltaic charge unit 70 is mounted on thewatercraft, when the charge in the energy storage unit 56 is depleted,or at/below a predetermined lower threshold, the system controlelectronics unit 62 will preferably continuously and automaticallyadjust the maximum K_(assist) value such that the power transferred tothe electric motor is originating from the photovoltaic charge unit 70,and therefore not further depleting the energy storage unit 56 to apoint of irreparable damage.

A significant advantage of this invention, relative to pure electricpedal watercraft (e.g., U.S. Pat. No. 6,855,016), is that in the eventof a motor or controller failure, the operator will still be able topropel the watercraft via pedaling. Conversely, the electric motorpropulsion unit can be easily configured to independently propel thewatercraft even if the operator chooses not to pedal. With an additionalswitch in the operator interface 58, the motor command can be changed insoftware in the system control electronics using 62 to be equal to, or adirect function of, the assistance factor, K_(assist); i.e.,

ω_(motor)*=ω_(prop36) *=K _(assist)   9

The operator then controls the speed of the watercraft by adjusting thevalue of K_(assist).

It should be further understood that the invention can be applied topropulsion systems for watercraft with virtually any type of watercrafthull design and construction, including planing hulls and monohulls, andeven hulls with hydrofoils.

The propellers 21 and 36 should be interpreted as any mechanism designedto produce propelling thrust for a watercraft including paddle wheels,rowing mechanisms, and moving fin mechanisms.

1. A propulsion system for watercraft comprising: a.) at least onehuman-powered propulsion means, b.) at least one electric motor-poweredpropulsion means, c.) the electric motor-powered propulsion meansconfigured to provide propulsion as a function of the state of thehuman-powered propulsion means, whereby the electric motor-poweredpropulsion assists the human-powered propulsion means.
 2. The propulsionsystem of claim 1, further comprising a sensing means configured toprovide a signal indicative of the state of the human-powered propulsionmeans, and a control means configured to receive said signal and tocontrol the state of the electric motor-powered propulsion meansaccording to said signal.
 3. The propulsion system of claim 2, whereinthe state of the electric motor-powered propulsion means is furtherconfigured to be a function of said signal and a motor assistancefactor.
 4. The propulsion system of claim 3, further comprising anoperator interface means configured to enable the watercraft operator toadjust said motor assistance factor, whereby the amount of propulsionassistance from the electric-motor powered propulsion means is adjusted.5. The propulsion system of claim 1, further comprising an energystorage means configured to supply electrical power to the electricmotor-powered propulsion means.
 6. The propulsion system of claim 1,further comprising a photovoltaic system means to provide power to theelectric motor-powered propulsion means.
 7. The propulsion system ofclaim 5, further comprising a photovoltaic system means to provide powerto said energy storage means.
 8. The propulsion system of claim 2wherein said control means comprises an electronics unit mounted withinthe housing of the electric motor-powered propulsion means.
 9. Thepropulsion system of claim 3 wherein said motor assistance factor ismodulated to simulate the travel through hills and valleys.
 10. Thepropulsion system of claim 2, wherein said signal is indicative of arotational speed of the human-powered propulsion means.
 11. Thepropulsion system of claim 2, wherein said signal is indicative of atorque of the human-powered propulsion means.
 12. The propulsion systemof claim 1 further comprising an operator interface means configured toenable the operator to see performance parameters and/or operatinginformation.
 13. The propulsion system of claim 1 wherein theelectric-motor powered propulsion means is further configured tooptionally provide propulsion independent of the human-poweredpropulsion means.
 14. A method of propelling watercraft comprising: a.)exerting human effort to provide a first propelling force, b.) providinga second propelling force via at least one electric motor-poweredpropulsion means, c.) sensing of said human effort, and d.) controllingsaid second propelling force based upon the sensed human effort, wherebysaid second propelling force assists said first propelling force toincrease the speed of a watercraft.
 15. The method of claim 14 furthercomprising providing a stored energy means to be used by the electricmotor-powered propulsion means to provide said second propelling force.16. The method of claim 14 further comprising providing a solar powermeans to be used by the electric motor-powered propulsion means toprovide said second propelling force.
 17. The method of claim 14 whereinsaid exerting of human effort comprises pedaling a human-poweredpropulsion means.
 18. The method of claim 17 wherein said sensing ofsaid human effort comprises sensing of the rotational speed of saidhuman-powered propulsion means.
 19. The method of claim 14 furthercomprising controlling the second propelling force by an operatoradjustable assistance factor.
 20. A propulsion system for watercraftcomprising: a.) a human-powered propulsion means, b.) an electricmotor-powered propulsion means, c.) the electric motor-poweredpropulsion means configured to provide propulsion as a function of therotational speed or torque of the human-powered propulsion means and ofan assistance factor; wherein the assistance factor is adjustable by theoperator, whereby the electric motor-powered propulsion means assiststhe human-powered propulsion means.